Max number of SDCCH depends on the TRX_Signalling configration. I suppose with TCUs you have Motorola BSS and in which RSL is normally 64K TS on the E1.
Now, remember this 64K RSL is for the entire site (i.e 3 sectors and 3 x No_of_DRIs per sector). For 2/2/2 config you should not have more than 1 sdcch/DRI or TRX (recommended).
Finally it depends on your RSL loading also.